Commit-ID: abcbcb80cd09cd40f2089d912764e315459b71f7 Gitweb: https://git.kernel.org/tip/abcbcb80cd09cd40f2089d912764e315459b71f7 Author: Geert Uytterhoeven <ge...@linux-m68k.org> AuthorDate: Fri, 22 Jun 2018 16:33:57 +0200 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Fri, 22 Jun 2018 17:48:36 +0200
time: Make sure jiffies_to_msecs() preserves non-zero time periods For the common cases where 1000 is a multiple of HZ, or HZ is a multiple of 1000, jiffies_to_msecs() never returns zero when passed a non-zero time period. However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 1024 or 1200, as used on alpha and DECstation), jiffies_to_msecs() may return zero for small non-zero time periods. This may break code that relies on receiving back a non-zero value. jiffies_to_usecs() does not need such a fix: one jiffy can only be less than one µs if HZ > 1000000, and such large values of HZ are already rejected at build time, twice: - include/linux/jiffies.h does #error if HZ >= 12288, - kernel/time/time.c has BUILD_BUG_ON(HZ > USEC_PER_SEC). Broken since forever. Signed-off-by: Geert Uytterhoeven <ge...@linux-m68k.org> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Reviewed-by: Arnd Bergmann <a...@arndb.de> Cc: John Stultz <john.stu...@linaro.org> Cc: Stephen Boyd <sb...@kernel.org> Cc: linux-al...@vger.kernel.org Cc: linux-m...@linux-mips.org Cc: sta...@vger.kernel.org Link: https://lkml.kernel.org/r/20180622143357.7495-1-ge...@linux-m68k.org --- kernel/time/time.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/time/time.c b/kernel/time/time.c index 6fa99213fc72..2b41e8e2d31d 100644 --- a/kernel/time/time.c +++ b/kernel/time/time.c @@ -28,6 +28,7 @@ */ #include <linux/export.h> +#include <linux/kernel.h> #include <linux/timex.h> #include <linux/capability.h> #include <linux/timekeeper_internal.h> @@ -314,9 +315,10 @@ unsigned int jiffies_to_msecs(const unsigned long j) return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); #else # if BITS_PER_LONG == 32 - return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32; + return (HZ_TO_MSEC_MUL32 * j + (1ULL << HZ_TO_MSEC_SHR32) - 1) >> + HZ_TO_MSEC_SHR32; # else - return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN; + return DIV_ROUND_UP(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN); # endif #endif }
